This invention relates to systems and methods for duplex printing of print sheets.
Printing on two sides of a print sheet (or print media or image substrate), referred to as duplex printing, is a desirable feature in printing systems because, for example, it allows the amount of paper needed for a particular print task to be reduced as compared with one-sided (simplex) printing. Duplex printing also allows print sets with layouts resembling that of professionally printed books to be generated. Conventional duplex printing devices often employ complex paper handling mechanisms. For example, in accordance with one duplexing method, an extra tray is used for temporary storage of a stack of pre-cut print sheets having printing on a first side. When a set of first side copies is complete, the copies are fed out of the duplex tray and returned with an odd number of inversions along a duplex path to receive second side imaging. Alternatively, the first side copies may be returned along a second paper path to receive second side printing without stacking.
High speed printing by xerographic, ionographic, ink jet or other copiers, printers, plotters or other reproduction apparatus (encompassed herein by the terms xe2x80x9cprinterxe2x80x9d and xe2x80x9cprinting apparatusxe2x80x9d) has become increasingly important and increasingly demanding in terms of quality, reliability, and other enhanced features, including full color and black and white printing functionality, and simplex and duplex printing functionality. High-speed printing machines typically print onto a web of sheet material, rather than using cut sheets as the copy sheets. The web of sheet material may be advanced from a roller through a printing module, which applies markings to the web of sheet material. Such roll feeding and printing systems may provide xe2x80x9ctwo upxe2x80x9d or xe2x80x9cfour upxe2x80x9d (duplex signature) printing, in which dual page images are printed in side by side pairs on one or both sides of a wide web (or large format) dual page width web of sheet material.
In general, duplex printing on continuous web substrates is much more difficult than printing on cut sheets. One continuous web duplex printing approach uses multiple opposing print engines for respectively printing on opposite sides of the web (see, e.g., U.S. Pat. Nos. 3,940,210, 5,701,565, and 5,455,668). Such multiple print engine web printing duplex systems, however, typically are characterized by substantial size, cost, complexity and maintenance requirements. In another approach, U.S. Pat. No. 5,970,304 has proposed a continuous web substrate duplex printing system that utilizes a single xerographic print engine. Separate first and second image transfer stations are positioned in line with one another in the direction of movement of the endless surface imaging member. The second image transfer station is positioned downstream of the first image transfer station. Each image transfer station respectively transfers print images to the first and second sides of the continuous web sequentially without requiring a dual width imaging member or dual imaging members. The two inline transfer stations may be part of a dockable web printing module that is configured to feed the continuous web into the print engine for image transfers to both sides of the web with web inversion. The system includes a web loop in between the two transfer stations for transferring the page print images onto both sides of the web in the proper sequence and positions.
Still other duplex printing systems and methods have been proposed.
The invention features systems and methods for duplex printing of print sheets in which print sheets may be controllably and reliably re-introduced into the print module in an orientation that is suitable for marking the second side of the print sheet without requiring a support structure that spans the entire width of the print sheet. In large format printing applications, the invention avoids large and heavy support structures, such as feed rollers, that otherwise would be needed to support the print sheets, as well as their own weight. In this way, the invention enables duplex printing apparatus of relatively light weight and a relatively small overall footprint to be implemented readily and in a cost effective manner.
In one aspect, the invention features a printing apparatus for marking first and second sides of a print sheet. The printing apparatus comprises a print module, a simplex module, and a duplex module. The print module is configured to mark one side of the print sheet at a time. The simplex module is configured to move the print sheet along a simplex feed path and to introduce the print sheet into the print module in an orientation suitable for marking the first side of the print sheet. The duplex module is configured to receive the print sheet from the print module. The duplex module also is configured to move the print sheet along a duplex feed path while clamping side edge regions of the print sheet and lo tensioning unsupported print sheet regions between the clamped side edge regions. In addition, the print module is configured to re-introduce the print sheet into the print module in an orientation suitable for marking the second side of the print sheet.
As used herein, the term xe2x80x9cmodulexe2x80x9d is intended to refer to a functional feature of a printing apparatus and is not intended to connote any particular structural implementation. For example, various modules of a printing apparatus may be incorporated into a single, unitary structure or they may be implemented as separable structural units that cooperate to perform one or more printing tasks.
Embodiments of the invention may include one or more of the following features.
In some embodiments, the duplex module comprises a print sheet handling assembly with sheet clamps mounted on respective rotatable arms. The rotatable arms may be configured to rotate about a common shaft. A first rotatable arm may have a fixed lateral position on the common shaft, and a second rotatable arm may have an adjustable lateral position on the common shaft to accommodate a width dimension of the print sheet.
In some embodiments, the print handling assembly of the duplex module comprises a cam surface system that is configured to control action of the sheet clamps during movement of the print sheet along the duplex feed path. The cam surface system may comprise a cam surface controlling separation of the sheet clamps during movement of the print sheet along the duplex feed path. The cam surface system also may comprise a cam surface controlling clamping of the sheet clamps when the print sheet is received from the print module and controlling unclamping of the sheet clamps from the side edge regions of the print sheet before the print sheet is re-introduced into the print module.
In some embodiments, the printing apparatus may be characterized by a footprint that is substantially smaller than the print sheet size.
The print module may comprise a sensor system that is configured to detect one or more holes in or edges of the print sheet for registering the first and second sides of the print sheet.
In another aspect, the invention features a printing apparatus having a duplex module that is configured to re-introduce the print sheet into the print module trailing edge first in an orientation suitable for marking the second side of the print sheet.
In another aspect, the invention features a printing method for marking first and second sides of a print sheet. In accordance with this inventive method, the print sheet is moved along a simplex feed path. The print sheet is introduced into a print module in an orientation suitable for marking the first side of the print sheet. The print sheet is received from the print module. The print sheet is moved along a duplex feed path while clamping side edge regions of the print sheet and tensioning unsupported print sheet regions between the clamped side edge regions. The print sheet is re-introduced into the print module in an orientation suitable for marking the second side of the print sheet.
In another aspect, the invention features a printing method for marking first and second sides of a print sheet. In accordance with this inventive method, the print sheet is moved along a simplex feed path. The print sheet is introduced into a print module in an orientation suitable for marking the first side of the print sheet. The print sheet is received from the print module. The print sheet is reintroduced into the print module trailing edge first in an orientation suitable for marking the second side of the print sheet.
Other features and advantages of the invention will become apparent from the following description, including the drawings and the claims.